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A053634 a(n) = Sum_{ d divides n } phi(d)*2^(n/d)/(2n). 6
2, 3, 4, 7, 10, 18, 30, 54, 94, 176, 316, 591, 1096, 2058, 3856, 7301, 13798, 26244, 49940, 95373, 182362, 349626, 671092, 1290714, 2485534, 4793790, 9256396, 17896284, 34636834, 67109898, 130150588, 252647064, 490853416, 954440950 (list; graph; refs; listen; history; text; internal format)
OFFSET

3,1

COMMENTS

Offset is 3 because a(2) is 3/2, not an integer. - Michel Marcus, Sep 11 2013

LINKS

G. C. Greubel, Table of n, a(n) for n = 3..3000

James East, Ron Niles, Integer polygons of given perimeter, arXiv:1710.11245 [math.CO], 2017.

FORMULA

a(n) = A000031(n)/2.

MATHEMATICA

a[n_] := DivisorSum[n, EulerPhi[#]*2^(n/#)&]/(2n); Table[a[n], {n, 3, 36}] (* Jean-Fran├žois Alcover, Dec 07 2015 *)

PROG

(PARI) a(n) = sumdiv (n, d, eulerphi(d)*2^(n/d)/(2*n));  \\ Michel Marcus, Sep 11 2013

CROSSREFS

Cf. A000016, A000031, A053635, A063776.

Sequence in context: A218495 A166012 A060166 * A094863 A094862 A104722

Adjacent sequences:  A053631 A053632 A053633 * A053635 A053636 A053637

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Mar 23 2000

STATUS

approved

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Last modified October 18 07:58 EDT 2018. Contains 316307 sequences. (Running on oeis4.)